1. Field of the Invention
One mode of the present invention relates to an electricity storage device and a structure of a negative electrode of the electricity storage device.
2. Description of the Related Art
In recent years, with the advance of environmental technology, power generation devices (for example, solar power generation devices), which pose fewer burdens on the environment than conventional power generation methods, have been actively developed. Along with development of power generation devices, power storage devices have also been developed.
As a power storage device, a secondary battery such as a lithium ion secondary battery (alternatively called a lithium ion storage battery or simply a lithium ion battery) can be given as example (see Patent Document 1). Lithium ion secondary batteries have high energy density and are widely popular because they are suited for miniaturization.
Similarly, as a type of power storage device, capacitors are being developed. As one of such capacitors, lithium ion capacitors can be given as examples.
As an electrolyte of the lithium ion secondary batteries mentioned above, a liquid electrolyte (called “electrolytic solution”) or a solid electrolyte is used. A nonaqueous electrolytic solution is normally used as the electrolytic solution, with which a high voltage which exceeds electrolysis voltage of water can be obtained. Also, as a solid electrolyte, a gel electrolyte or a polymer electrolyte can be given as examples. When a solid electrolyte is used, there is an advantage in that leakage does not occur easily compared to an electrolytic solution.